Strukturuntersuchungen an adsorptionsschichten makromolekularer stoffe, 1. Haftstellenzahlen von linearen polyestern und polystyrol an aerosiloberflächen

By direct IR-spectroscopic determinations of the fraction of attached segments and of the adsorbed amount of linear saturated aliphatic polyesters, of polystyrene, and of butyl propionate, when adsorbed from dilute solution onto Aerosil silica, the structure of the adsorption layers is described. The polyesters are hydrogen bonded via almost all carbonyl groups to up to 80% of the free hydroxyl groups of the Aerosil surface as far as free adsorption sites are available. They form a layer structure consisting of small loops. Variations of molecular weight and chemical nature of end groups of the polyesters do not affect their adsorptive properties. By contrast, only every third aromatic nucleus of polystyrene interacts with the surface of the Aerosil silica. Like the model monoester, polystyrene is not capable of interacting with more than 50% of the surface hydroxyl groups. The adsorption data obey Langmuir's equation. Furthermore, they are in good agreement with the predictions of a statistical theory of Silberberg for polymer adsorption with strong adsorption interaction. The determined fractions of attached segments are compared with the considerably lower values in the literature and are discussed on the basis of the average distances of surface hydroxyl groups, statistical distribution assumed, and the calculated maximum distances of adsorbable groups in the polymer chains.